Page Fault Scalability patch V19 [4/4]: Drop use of page_table_lock in do_anonymous_page

[Christoph Lameter <clameter@sgi.com>]

Do not use the page_table_lock in do_anonymous_page. This will significantly
increase the parallelism in the page fault handler in SMP systems. The patch
also modifies the definitions of _mm_counter functions so that rss and anon_rss
become atomic.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.11/mm/memory.c
===================================================================
--- linux-2.6.11.orig/mm/memory.c	2005-03-09 10:43:28.000000000 -0800
+++ linux-2.6.11/mm/memory.c	2005-03-09 10:43:29.000000000 -0800
@@ -1825,12 +1825,12 @@ do_anonymous_page(struct mm_struct *mm, 
 						 vma->vm_page_prot)),
 			      vma);
 
-	spin_lock(&mm->page_table_lock);
+	page_table_atomic_start(mm);
 	
 	if (!ptep_cmpxchg(page_table, orig_entry, entry)) {
 		pte_unmap(page_table);
 		page_cache_release(page);
-		spin_unlock(&mm->page_table_lock);
+		page_table_atomic_stop(mm);
 		inc_page_state(cmpxchg_fail_anon_write);
 		return VM_FAULT_MINOR;
 	}
@@ -1848,7 +1848,7 @@ do_anonymous_page(struct mm_struct *mm, 
 	SetPageReferenced(page);
 	update_mmu_cache(vma, addr, entry); 
 	pte_unmap(page_table);
-	spin_unlock(&mm->page_table_lock);
+	page_table_atomic_stop(mm);
 
 	return VM_FAULT_MINOR;
 }
Index: linux-2.6.11/include/linux/sched.h
===================================================================
--- linux-2.6.11.orig/include/linux/sched.h	2005-03-09 10:43:26.000000000 -0800
+++ linux-2.6.11/include/linux/sched.h	2005-03-09 10:43:29.000000000 -0800
@@ -203,10 +203,26 @@ arch_get_unmapped_area_topdown(struct fi
 extern void arch_unmap_area(struct vm_area_struct *area);
 extern void arch_unmap_area_topdown(struct vm_area_struct *area);
 
+#ifdef CONFIG_ATOMIC_TABLE_OPS
+/*
+ * Atomic page table operations require that the counters are also
+ * incremented atomically
+*/
+#define set_mm_counter(mm, member, value) atomic_set(&(mm)->member, value)
+#define get_mm_counter(mm, member) ((unsigned long)atomic_read(&(mm)->member))
+#define update_mm_counter(mm, member, value) atomic_add(value, &(mm)->member)
+#define MM_COUNTER_T atomic_t
+
+#else
+/*
+ * No atomic page table operations. Counters are protected by
+ * the page table lock 
+ */
 #define set_mm_counter(mm, member, value) (mm)->member = (value)
 #define get_mm_counter(mm, member) ((mm)->member)
 #define update_mm_counter(mm, member, value) (mm)->member += (value)
 #define MM_COUNTER_T unsigned long
+#endif
 
 struct mm_struct {
 	struct vm_area_struct * mmap;		/* list of VMAs */